﻿Shader "RoKiShi/SnakeShader"
{
    Properties
    {
        _MainTex ("Texture", 2D) = "white" {}
        
        _GridX ("Grid X", float) = 32
        _GridY ("Grid Y", float) = 32
    }
    SubShader
    {
        // No culling or depth
        Cull Off ZWrite Off ZTest Always

        Pass
        {
            CGPROGRAM
            #pragma vertex vert
            #pragma fragment frag

            #include "UnityCG.cginc"

            struct appdata
            {
                float4 vertex : POSITION;
                float2 uv : TEXCOORD0;
            };

            struct v2f
            {
                float2 uv : TEXCOORD0;
                float4 vertex : SV_POSITION;
            };

            v2f vert(appdata v)
            {
                v2f o;
                o.vertex = UnityObjectToClipPos(v.vertex);
                o.uv = v.uv;
                return o;
            }

            sampler2D _MainTex;
            float _GridX;
            float _GridY;

            

            fixed4 frag(v2f i) : SV_Target
            {
                fixed4 col = tex2D(_MainTex, i.uv);

                float2 scrPos = i.vertex.xy;
                float2 scrSize = _ScreenParams.xy;
                scrPos.y = scrSize.y - scrPos.y;
                float2 grid = float2(_GridX, _GridY);
                float2 fullGrid = scrSize / grid;
                float2 scrGrid = scrPos / grid;
                scrGrid.x = (int) scrGrid.x;
                scrGrid.y = (int) scrGrid.y;
                float2 gridPos = scrGrid / fullGrid;

                return fixed4(gridPos.xy, 0, 1);
            }
            ENDCG
        }
    }
}